Main reason is that they are turning him into Cena II
I have 3 reasons for disliking
1. He beat Daniel Brian in 18 seconds at Wrestle Freaking Mania. If it was a Smackdown match it would not have been as bad but this was Wrestlemania and whoever thought this was a great idea is an idiot (even Vince if it was his)
2. Long title reign. Faces and long title reigns DO NOT WORK. The faces are supposed to be chasing the title. If he's beating the shit out of everyone, why the fuck would I want to feel for him and cheer him?
3. No character motivations. What the fuck is he? A guy that says fella all the time and smiles like an idiot? When is the last time someone really pissed him off? Back in the days, the big faces (by big I mean in size) were usually ganged up by factions. Let's use Undertaker for an example. How to antagonize the Undertaker when he was a face during his American Badass days? -Stalk his wife, fuck with his bike, screw him out of a match every now and then, beat the crap out of him with a chair, injure his hand. When is the last time we saw a storyline injury?

Honestly Sheamus should have lost the title in July/August. Dolph Ziggler could have had a nice summer run and then lost it in October/November back to Sheamus or to someone else who then would lose to Sheamus. This is exactly what killed Cena in the first place. Forcing him down our throats. The WWE doesn't seem to learn from their mistakes. Cena could have been the best face of all time if they had built him right.

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